Be playful Be consistant (watch those backslides) Demonstrate to him that you love him, but don't need him (great opportunity while you guys are living together/separated).
The female/work colleague thing is a bit dodgy - the thing for you to remember is that he's getting his "emotional" needs met from this woman. The more lighthearted, fun, un-needy you can be the better. You may be able to create an environment of trust, where he might just find it nicer to get his "emotional" needs met from you.
Emotional Affairs are tricky. Often there is no sexual stuff going on - often the whole attraction of an emotional affair is that it's safe (colleagues, internet affairs that are long distance – the kind of ‘relationship’ you can have without having a ‘relationship’) – but forging friendships outside of the marriage, no matter how platonic, isn’t really OK.
Still – it’s out of your control girlfriend – so you need to let it go for now. .
V
Never make someone a priority, who makes you an option.
