I haven't read the issue, just heard some of his behavior in this arc, but that doesn't sound out of character. Specially since I heard that in this arc he's... focused on sex.
It's definitly not a healthy choice, but he's not exactly a healthy person in a healthy situation, from what I gather.
Newley souled, a bit lost, without direction I suppose, been killing bad guys and girls for months now.
Of course, it's hard to say what is and what is not out of character for Spike. We haven't gotten to know him very well, not well enough for me to say what he would or wouldn't do. I've seen the nice side, the cocky side, the funny side, the loyal side and the heroic side of this "new" vamp, and kind of want those to be his only side, but the demon is still in him, and for all I know (not having read past issue 27) he got noone around him that will tell him to "behave", or that he feels the need to impress. If Buffy or Fred was around, he might not have slept around at all, specially not with a girl he plans to kill, but noone's there for him. I don't blame him for doing that.
I might change my mind when I catch up with the series, but I'm not that surprised. I'm not even sure if I would be surprised if he rapes bad guys then kills them. I have no idea where he is emotionally right now, but I'm guessing he's indifferent or/and or hurting.