Are you totally happy with what you are getting with Guy Number One? And you may be...if you are, dandy.
If not, you owe it to yourself to get to know any other people who interest you. Heck, you owe that to yourself anyway. I don't mean this flippantly. I REALLY mean it. If you want to get to know Guy Number Two, please do. It doesn't mean you're making an irrevocable choice yet.
"My predominant feeling is one of gratitude. I have loved and been loved;I have been given much and I have given something in return...Above all, I have been a sentient being, a thinking animal, on this beautiful planet, and that in itself has been an enormous privilege and an adventure." O. Sacks