Most Helpful Guy
First off. How the fuck did you get your words to be italic, I mean I wanna do that shit too. Second it's best to tell him but don't hope to make him jealous because if he becomes jealous he most likely isn't the type of guy you'll want to date. Telling him would save him the trouble of preparing for the date and he won't hate you for blowing him off (No pun intended).
Most Helpful Girl
Can't you change your plans for Monday and see him? If not, looks like you should move on and let him know that presently this relationship isn't working for you. Also, maybe he doesn't want to rush things as he wishes to be more settled in life, socially, health-eise etc that's why he isn't giving you lots of attention. Maybe? He just doesn't seem certain about you or his own life at this point. Initially felt like telling you take the opportunity to meet him but also meet the other guy as truthfully I don't know how it will work out. However, I guess he'll figure out it's over when you refuse to meet up. TBh, I think you already made your decision, so best forget him now.