I was with a really terrible person. He was my first adult relationship and he betrayed my trust so many times that I lost count. I eventually left him and cut him out of my life, but I still find it difficult to trust anyone. I don't trust anyone completely. I find myself overthinking a lot about if my family really loves me, or my boyfriend, or if anyone cares about me at all. 4 months after leaving that terrible person, I met and started dating a new guy. Unlike my ex, my boyfriend treats me the way I want to be treated and loved. He doesn't hurt me in any way. If I have a problem or if he makes me feel any negative emotions, I just tell him and he apologizes and doesn't do it again or changes it so I'm happy. I've never been with anyone like that, but I still am having difficulty trusting him. We've been dating 7 months now and I've never caught him flirting or cheating on me. I found it difficult not to worry when he was talking with all these friends he had on facebook that were all gorgeous women, so he unfriended them because he didn't want me to feel that way. I'm trying to work on my issues and I can say I've only ever asked to see his phone once. I know I shouldn't do that and it's seen as toxic, but I needed to see it at least once to know if he was really trustworthy. I was so anxious to see his phone and I did see that he has been using snap chat. It's a social media app that is fine, but it deletes your messages with someone automatically and allows you to send temporary pictures that also get deleted. I saw he had deleted all the girls except for one that he said was a good friend that he didn't want to lose. I felt bad and I didn't want him to lose his friend. I told him fine and that was it. I saw when I went through his phone though that he messaged her through snap chat. He only uses facebook messenger, even with me when he has my number. I thought it was weird that he only messages her on snap chat because she has a facebook messenger. I try not to think about it. I'm really trying to trust him. He's told little lies before and I've forgiven him because he's human and he's promised not to again and hasn't since he lied last about 2 or 3 months ago. I don't know if I should ask him to delete snap chat, ask him to delete her off snap chat, or choose to trust him and ignore the problem and worry about it sometimes.  Any advice on trusting, not worrying, and this situation specifically would be great.

You are victim of toxic relationships and you still didn't fully recover.
It's normal, don't judge yourself.
No one deserve to be treated that way.
Read this https://shinymotivation.com/its-time-for-a-change-motivation-to-leave-a-toxic-relationship/ and compare your actual relation.
If there are no traces of toxic relationship you are good to go, and it will take time, don't worry it won't happen instantly.

You seem like a very genuine person with a natural feel of curiosity about your boyfriend, that’s great because apart from everybody feeling intimated from their man or lady messaging other people it wouldn’t be hard for you to take it easier on the situation

I feel as much as saying that all of your insecurities with your boyfriend could change if you just have better intellectual conversations about the problem that’s on your mind with your boyfriend. You would then have to put your foot down and come out to him about how you are feeling deep down. I would definitely not bring up the topic in a strong argue type way but steadily and easily bring up the topic and with good conversation taking place the both of you will continue to solve the problem.

Comfortability = BEATS BAD FEELINGS

Both of You must come to an agreement with your boyfriend about what he has to proceed in order to gain your trust, it could be “Deleting Snapchat” giving you the “password” anything that opens up and gives you complete security

Most of these “sharing” would definitely not be surpassed without the emotions of comfortability.

And let me tell you, if he has no comfortability in giving you his shares of own, at 7 months the man would definitely not be worthy of your time, keep loving and always think positive