I keep catching my boyfriend involved with other girls, halp D:?

[Bleh Um]

This might be a bit long but here goes, I am in desperate need for advice. So my boyfriend and I have been in a long distance relationship since 2 years and things have been slightly bumpy. (I am 20 and he's 26, not that it should matter but just in case) It started like this, in the first 3 months i wanted to be a bit attention whorey and flatter myself so i logged his facebook to see what he had been telling his friends about me but I found him flirting with girl A. I confronted him and he said sorry and that he wont do it again and i was like okay no problem, she was cute it's understandable and moved the eff on.
After that a few months later say 8 months into our relationship I caught him stalking girls on facebook (through search logs, again wanted to flatter myself I should prolly quit doing that soonish) he would repeatedly search for Girls B, C and D repeatedly day in and day out, especially girl B he was like constantly searching for her. So yeah I confronted him, we had a huge fight but he begged me to take him back and I did.
Now a few months ago i was in a bad phase financially because my dad resigned from his job and our finances were mighty unstable. So I used to feel low. When we had a fight he met this girl D through a dating app called tinder and they made plans to meet but he says he didnt meet her because he realized it was wrong. I just found out about this yesterday and I am a bit shaken cause it is hurtful how he keeps straying.
So we are together as of now he leaves for America in 5 days and he has never physically cheated on me or I actually have no clue if he has he has lied to me about never being involved with other girls but would frankly consider this being involved. He keeps asking me to trust him and that he loves me he cried a lot today but I dont know what to do. Is it safe to trust him after how he repeatedly strays away like that? I don't want a future where he might do this again because it's scary. Things were pretty serious to the point that we almost got engaged but stalled because I couldnt give him my ring measurement in time because of schoolwork and Im sort of glad that happened because I have developed trust issues and I really don't know if I can and should trust him again.
Sorry for the long wall of text and thanks :X

[Kenzie]

You sound much younger than twenty. You should probably put off marriage for a variety of reasons.

[Danielle]

Sometimes guys just need to know theyve still got it. Words/messages (that u shouldnt b reading/ invading his spacee,) shouldnt bother u as long as his actions say hes not cheating.

[Cristian]

No, he shouldn't be doing this. If he's with you, he shouldn't, no matter WHAT, flirt with other girls. And he wanted to meet with one of them! You need to do something to let him know that it bothers you, how you don't want him to do it anymore, and if he does, you need to dump this douche. If he really loves you, he would do anything to make you happy, and stop doing things that scare you.