u/Chelitosuav

My girlfriend and I have been together for 3 years. And recently i started the process of planning to engage. But recently information came to light that brought back 1 worry of mine. That it seems to a repeating factor... When we first started dating we had an argument about her hanging out with a guy who had asked her out 3 times and she claimed he was just a friend..... as well as wanting to hangout with an older guy she admitted to at one point she was trying to sleep with him... After that I realize she lied to me 3 times about her ex... She had him on socials still kept pictures of him.. and still texting one of his family members... I said " why are you keeping tabs on him?" She claimed she wasn't... and I told her that's weird and i feel like you are hung up on your ex..... Then before the start of the new year we had big argument. She said she was losing attraction to me. And while in the car said " He looks good out loud". i ASKED "Who?" It was her ex.... and she was talking to him and texting him..... She said she blocked him after that argument.... claimed.. but he still on her facebook... and pretty sure still on instagram... And now she told me passingly recently a guy asked her out.. He was cool to talk to... and then when she told him she had a boyfriend he blocked her.... But her response to him blocking her was "oh okay".... As if it didn't make sense to her... Mind you she is in college still.. and she says she is busy which is why she can't respond a lot through text. But when I am with her she responds to her friends and people on her phone so fast. And checks her phone constantly.. She says that when she spends time with me that's actually time she has to get back to people... But like anytime she isn't with me she takes for ever to reply. But somehow this guy got know her enough to take an interest....Every now and then we will have regular phone calls before bed but she isn't very talkative I always have to try and get her to talk about stuff.....I am having doubt about proposing I fear this girl will cheat.... She says she still doesn't understand why talking to her ex was bad... Am i wrong to question her on this?

She has been officially diagnosed ASD LEVEL 1 AND ADHD. Don't know how much this affects not understanding social cues and what okay and not.

TLDR:

I am worried that if I marry this girl she will cheat on me based on previous arguments and recent actions. That have me suspicious. Am I wrong for cutting her off from her ex? Am I wrong for questioning whether i should marry this girl?

Any advice as to whether I should actually pursue marriage with this girl?