Magi-Chan seems to have some inconsistent behavioral tendencies even in TRS, but I think Blank does this on purpose because while Magi is the absolute master of the mental realm and playing the puppet/chess master he totally sucks at aspects of the physical realm such as direct confrontation. He reminds me of the Pokemon Abra and its evolutions, like them he's a creature with a weak spindly body and a glass cannon who absolutely can't take physical hits, but makes up for all that by having an extremely high special attack.
In regards to his sex life (sorry Magi...), in the main story line he totally comes across as a love shy virgin who was playing the waiting game, thinking Silvana would eventually come (back) to him and proceeded to have a breakdown when she did come back and revealed she had a girlfriend and was not interested in rekindling their romance. But fortunately he starts a thing with Spunky soon afterwards, who seems to be his "first." However in the current story line he seems to have no problem getting sex when he wants it and even revealed right before this story line started that he has the ability to tap into other people's sex lives. At first I was confused by this seemingly glaring inconsistency, but it makes perfect sense when you realize that what he was initially going to have with Silvana, and what he succeeded in having with Spunky, is TRUE AND HONEST consensual love without the need for hate fucks, manipulation, hookers etc. TL;DR Magi can cheat to get whatever he wants, but it's only really worth it to him if he can get it honestly and the love his partner has for him is mutual.