how could i (37f) possibly trust my bf (36m) again?

i (37F) met my bf (35M) at work. we’ve been together for 3+ years. we had a break for two months late last year, with the intention that he would figure out what he wants to do with his life.

instead, he used the job to meet more women. one of which, he asked her to marry him. he says this woman is his “friend” (aka talks to her for 15 minutes every two weeks). he continued to use the job to connect with more and more women to possibly date

after many conversations and plans to check in more often moving forward, we got back together. (i know these aren’t great reasons, but he’s already integrated with my extended family, all of my friend circles, and we’re have basically been living together for 1.5 years)

he had to go to the hospital the other day. urgent care required he be taken by someone. he called me once, but i forgot my phone at home. his second call was to this “friend”.

i had absolutely no idea he was still in touch with her. i’m very transparent about who i talk with, plans, and contextual info about anyone i hang out with

when i retrieved my phone coincidentally a few minutes later, i come to find that id better hurry to pick him up or she will be his liaison to the hospital.

he doesn’t have any friends, so he felt calling her was his “only option”. i asked why he didn’t call the job or a plethora of people he knows in his neighborhood, he said he “didn’t want to bother them”. however, this “friend” doesn’t live in his neighborhood, is apparently married, and he calls her next. he also claims he thought of her because they were texting earlier in the day about “the man she married” needing a job.

after this fiasco, i came to find out that in april (we were together, not on a break) he had a whole conversation with her about the fact that she didn’t answer his proposal. he consistently maintains “i didn’t cheat” or “that was last year” or “it’s my fault i can’t satisfy him” or “if i say cheating i need to include the ‘emotional’ part.” all of these just feel like excuses upon excuses to gaslight me and avert attention from his wrongdoing.

he did apologize about the hospital call, but he never did about this secret conversation they had.

to give you an idea, here was my bf’s last message to this girl in the deleted text thread.

“Honestly, I have to tell you that you're my type. You have everything I like in a woman: your way of speaking, your smile, your body language, etc. Plus, you have all the qualities a man needs in a woman! Sorry if I went too far, but I had to admit it. Let me know if you found anything good or bad, and I'll always be kind and respectful of you.”

TL;DR my boyfriend tries to connect with only women(sometimes at our shared workplace), seemingly in hopes they can be a backup for him later. whenever i try to confront it, he gets furious and finds a way to blame me.