P.s. I'm very upset right now so any criticism you have can you please word it nicely so I don't overreact anymore than I probably already have. That would be very much appreciated.
Most Helpful Girl
Do you know if it's a girl he knows in person? He may have just gotten it from one of his guy friends (who was being kinda jerky if that's the case) or from the internet or something. In those cases, no it's not great behavior. Even those things might be considered rude or intolerable depending on the 'rules' of your relationship.
However, I would not jump the gun and automatically assume he's cheating. Furthermore, I would definitely not be overly aggressive about finding evidence. Once you start doing that, the relationship is over. If he's cheating or not, you've forfeited the relationship, because it just adds a whole level of deception to the thing and he'll probably catch you snooping around. If someone is genuinely concerned that their partner is cheating - to the point where they are very tempted to snoop and try to catch the person in a lie - it would be better for them to simply be honest with the person, and say "I really like you, and maybe you aren't, but I can't get over the suspicion that you're cheating, so I'm breaking up with you, so I'm not tempted to invade your privacy in order to find evidence of cheating."
I would drop the subject for now. The more you question him, the more he'll become entrenched in his position. If he IS lying, asking him, "are you sureeee?" is only giving him practice in lying. Drop the subject. Wait to see if something else fishy happens. Gauge his FIRST reaction to a situation like that, and that will give you the most truth.
I definitely wouldn't be thinking about marriage with this person, at least for right now, because your relationship is not on solid ground right now.