Should I be concerned?

Recently I was unsubscribing & deleting emails and saw ask.fm notifications. Went in to deactivate it and saw that 6 months ago someone anonymously asked how I found out my boyfriend was cheating on me. This is a first I’m hearing of this. It could be nothing BUT:

1.) 6 months ago we were constantly arguing, not having sex.

2.) I was traveling for work around that time.

3.) I told two relatives & no one else that we were having issues.

4.) I’ve had issues with him communicating with his ex, who claims to be happily married, yet always stirs up conversations about me and when he and I will be getting engaged/married.

Also the same ex who he was sleeping with while she was supposedly in a committed relationship with her now husband.

I confronted him about this tonight, which he did not deny just said “Anyways” and ignored it. Which makes me uneasy. I’ve been cheated on in a previous relationship & not trying to deal with that again and I’m also right of a work trip.

How do I get to the bottom of this???I