@babybird,
And ... how should/can we help you out?
Far as I can tell - distilled version of the original post.
1) You have a serious bf who is about ready to pop the question. His family's happy, you love him, it all feels great.
however
2) During time apart (a break, a separation, dunno what it should be called), you date Tom. This involves affection, I have no idea how much from what I'm reading, e. g. whether it's a few kisses or sex or something in between.
3) After reconciliation, you tell your bf (who is upset about the whole Tom thing) that you'll never contact Tom again.
4) However, you learn through the grapevine that Tom is being deployed, Tom is getting married, etc. Hence you contact Tom, in a complete 180 from #3.
5) Tom comes over. There is kissing involved.
Now what?
Well, let's reverse the names and the genders. You have someone you love and you want to spend the rest of your life with them. They have some time with someone else but it seems, at least under a technicality, to not be cheating. You ask for them to sever all contact with that other person and they agree. But for whatever reason, they cannot leave well enough alone and they betray you by breaking their promise and contacting that person and then they further compound said betrayal by kissing said other person.
You have -
1) lied about severing contact
2) maintained contact info at least in your phone, thereby providing a means of making contact. Anyone serious about severing contact would have deleted phone numbers. You did not. This is a deliberate act; you never meant to sever contact, now, didja?
3) you then made contact
4) and escalated it to in-person contact
5) and then escalated it again to kissing contact
Do you tell your boyfriend?
Yep.
Why?
So he has the information necessary to determine whether he wants to stay with you, or strike out on his own. If he were the one doing the asking, after having been told by you, I would tell him to leave you, as you have proven yourself untrustworthy on several occasions. Sorry, but that's life in the big city. This is a lesson you need to learn.