This was discussed before at some length but it's been a while so I'll go ahead and throw in my two cents.
Does Gin love Matsumoto? I don't think he loves her in the... normal sense of the word. We all know Gin is not a normal person, anyway -- his emotions and intentions are all veiled in mystery by that fox-face expression and his casual, sneaky behavior. And, yet, the only time that I've seen his face express something sincere was the time when he was leaving for Hueco Mundo, and he looked back to Rangiku and said simply "I'm sorry." For all that he did, the last thing you'd expect is for him to be apologetic about anything.
I believe that Gin's feelings for Matsumoto are strong enough to the point that he does not truly wish harm upon her. True, he did set Kira up to fight Hitsugaya and Matsumoto if the need arose, but even to Aizen, Gin referred to Izuru as a mere "distraction." I think he knew that Kira would not be able to stand up to the likes of Matsumoto, but needed him to buy him as much time as possible to keep Matsumoto away.
As for his behavior of waltzing in and out of her life, I believe that while he cares for Matsumoto, I think he wants to keep her away at a safe distance so he could never hurt her or use her for his grand scheme. It might be a little too much speculation on my part, but it does make sense (or at least to me). Think about it, the others that had been closely associated with him (excluding Aizen of course) were hurt and/or used by him. However, when faced with Matsumoto, it seems as if he either:
1) Runs away (such as the case when she intercepted Shinsou's attack during the fight with Hitsugaya or all the times we've been told he walks out on her),
2) Confuses her (not telling her why he keeps leaving, speaking to her kind of sarcastically when he left "If only you could have held onto me longer...")
3) or, speaks with what little sincerity he has. ("I'm sorry," or as he sings in the musical "Thank you for everything and goodbye")
In conclusion I believe that Gin does harbor feelings akin to love for Matsumoto. He so damned eccentric, however, and is not capable of loving her as a man should. Tragically Matsumoto does care about him enough to the point that his behavior leaves her emotionally wounded and confused. The lyrics to the character song "Fuyu no Hanabi" describe it perfectly:
I think this the same argument as I made before, too. Maybe there'll be more input from others this time.