advice needed

On/off since middle school, both 17. We talked about marriage and kids and stuff.

What do I do? I feel like I sabotaged this because six months into our relationship (we broke up and got back together), she started a TikTok streak with a guy I remember from her past. She still kept the streak with him for over 100 days. I don’t know what they would talk about, but in the comments of her videos, he would be really flirty with her. He would say a lot of sexual things to her, and I was really jealous because it seemed like they had something going on. She would reply to it. He even commented 'marry me,' and he’s under every video. She is attractive, and I know now that some people will just act in certain ways when that happens. So maybe it was just a streak, and he made it seem as though they really did.

But look at this: the reason I think that I sabotaged it is because I got jealous, and at the time, I didn’t know what to do when I felt jealous. So I just followed 10 girls and I put heart eyes on two of their videos publicly because it was a reaction to what she did. But look, after I did that, we got into a huge argument over something unrelated, and I later looked at her account and she commented on his post and said, 'this my man😍' or something along those lines. Then later she started to devalue him publicly too. She was very inconsistent in the middle of our relationship, so it really made me feel bad because I was always consistent until the end. I just reacted to what she was doing, but in a bad way. What do you guys think though?