<human>: Can you condense the text into three sentences or less?

Basically we've been together quite a while, he's talked at times about getting married someday and has told me he has an idea of how he's going to propose. I've never had any reason to not trust him and I've always trusted him completely. He went to Europe at the beginning of the semester for 6 weeks for school reasons with some of his friends in his major. I heard rumors when he came back that he tried to "get with" one of the girls while he was there. He denied that anything happened except some "regretful" (and unsuccessful) advances he made towards her. He said he was just lonely and he made a mistake. I believed him but I lost some trust in him.

Recently, he's been hiding his computer and phone whenever we're together (I've never gone through any of his things so this is odd to me) and he seems to be constantly texting one of his other girl friends (which is not normal behavior). They hang out quite a bit when I go to work and am busy and now that I trust him less since he came back from Europe I'm very worried. I don't know how confront him. I feel that confrontation would just end badly. He tends to shut down completely and not communicate when I confront him about anything. What should I do?
<bot>: Lost some trust in my boyfriend after I learned he had made advances towards one of his girl friends while he was out of the country. Now I think he's cheating with a different friend and I don't know how to confront him.