Can a breakup be so big to affect mental health for over 16 years?

have been married since 9 years.Ours was a love marriage. He had a previous relationship in high school. His girlfriend had broken up from him long time ago before we met. Before marriage he has told me that he was really affected by that breakup and was very emotionally damaged. When we got married she started contacting him(she got married 2 years before us and was married with kids at this time).

He will always talk to her and will hide it from me even though I told him so many time that its ok and if he wants to talk to her he can tell me and can even talk to her in front of me. But he will always hide it from me and one time when she called and i told him to pick up, when she noticed i am next to him she became uninterested in talking and told him to call later. At first he told me that she says she regrets breaking up with him and my husband told me he feels better hearing this and that is the reason he talks to her.

Over these 9 years this has been happening again and again approximately 2 times a year and every time i catch him hiding it from me. I had my first baby and few days later he was talking to her at night for 3 hours while i was struggling with the baby. When i caught him again he told me she was educating him how to handle a baby and all other excuses.

At one instance he lied to me about a business trip to another country and traveled to her country (at this time she was living in another country) to meet her . When i got to know the truth i called her husband and he caught them in a hotel when they were about to meet. He came back the same day and made an excuse that he was going through so much of work load that he wanted to just go somewhere and this came as an opportunity as she asked him to meet once. He promised me that he will never talked to her again. 1.5 years and 2nd baby later i again caught him hiding and talking to her at night.

I am so confused right now that these are the times that i have caught him and eveytime he tells me that he has been talking only for 2-3 days but i feel what if i do not catch him he will continue and whenever i catch him he will tell ohhh its only been 2-3 days. Other than this my husband is a good person he is a good father he earns very well and has always been so intelligent and a high achiever. But my confusion is the excuses he is making that he has no control over his mind and that this ex girlfriend always manipulates him in talking to him by talking about her difficulties in life that she doesn’t have a good husband ( which is a lie i have talked to her husband he is a simple and mature man earns good ).

Am i making a fool out of myself by trusting him again and again and being betrayed repeatedly? And its just because i love him i trust whatever he says sometimes it doesn’t even makes sense. His excuse is that he is wired and build differently from other people. Please suggest what should i do. Any suggestion will be helpful i feel so low at this point of my life.

PS :- 7 months later

He went to Thailand again. This time he had a business trip there and that ex girlfriend of his visited him there.

I was home for 9 days with kids. When he went everything was normal I had no idea he was talking to her and was in contact. The day he came back I saw him sending some messages, I asked whom is he talking to he snatched the phone away from me and told me it was nothing. I cried and begged him to tell me what is going on he told me nothing. Next morning when he was in the bed in another room I went to lie down with him, his phone was in his hands the phone rang and it was her. I took the phone and told her do not hang up I want to talk to you. I asked her what is going on? If you guys are friends then why all this hiding? She said “we are definitely not friends, you should understand yourself that if it has been happening since 12 years then we can’t be just friends”. I was in deep shock. She continued “Me and your husband we have decided something, he will tell you’. When I asked her she told to put the phone on speaker and she said “we have decided we will keep talking and see where it goes and once the kids are grown up maybe we will get together”. My husband was silent through all this. When I hung up the phone he told me she was lying and he has not said anything. He told me he will not talk to her now.

After 4 days I again discovered text messages from my husband that mentioned about them meeting in Thailand, he wanting to get her smell from the t shirt he was wearing when he met her. I confronted him and first he tells me that he fell in love with her 3 months ago. After 15 mins he changed his words to that he was not thinking straight. He promised again that this will not happen. Then he started to be transparent to me showing every message that she sends ( also deleting some which I found out) when he refused talking to her she started blackmailing him sending pictures from Thailand. My husband has started therapy and the therapist told him that he has a self love deficit issue. That is why he is attached to her and seeks validation from her. And hence this relationship of his has come this far.

I have decided to stay with him but I continue to wonder that this mental health term can justify everything that happened?