Thanks for writing to Just Answer.
You didn't mention if you lived with your boyfriend or not, so I'm going to answer as if you're not. If you are, double the intensity of everything that follows:
The first thing to ask yourself is if you were feeling "tied down" to your boyfriend before the other guy came into the picture.
If so, it may be time to take a good look at the relationship. Just the fact that you chose the phrase "tied down" may be an indication of how you've been feeling.
However, you need to know that your current relationship is 98% sure to end if you tell him you want a break.
Imagine that your bf came to you and said he had met someone, and wanted to find out it that other relationship can work. If the very thought of him being with someone else is upsetting, then think carefully before ending it. If the thought brings relief, then you know it's time to leave.
I would caution you against leaving him "for" someone else. There are no guarantees that the other guy is as wonderful in private as he is in public. Some of the most controlling, horrible husbands are men who everyone (but their wife) thinks is wonderful.
He's also leaving. Are you thinking you will pack up your life and follow him?
The one thing I always ask my clients to do when they are feeling a vague dissatisfaction with their relationship, job, etc is:
For one week, the very first thing in the morning (before you shower,even) get up and immediately sit down at your desk and hand-write (don't use a computer) three pages of free-flowing, stream-of-consciousness journaling. Don't stop moving the pen, even if all you're writing for half a page is "I have nothing to write" over and over. Sooner or later, your subconscious will emerge, and things will come pouring out (usually after about one and a half pages.
Why do I recommend this? Often when we have a vague, nagging sense of discontent, it has more to do with ourselves than with our partner. Is there something you want to accomplish but haven't? Are you stuck in a job or in a major at school that doesn't fit you?
What's important is that you don't pin your hopes of a better life on some new guy...this could start a life-long pattern and leave you twenty years later with a string of broken relationships and wondering what happened to that great guy you dated for 3 years back in the day.
I just have a feeling that what you said: "I can't help wanting to see what else is out there"
has more to do with your life than with your relationship (notice you didn't say "who else"..you said "what else").
This is all to encourage you not to do anything rash because the other guy is leaving soon. This adds a false sense of urgency which could pressure you into making a decision you'll regret later on.
I hope I've given you some new ways to think about what's going on...
I wish you the best, XXXXX XXXXX what you decide,