Last year, my manager asked me to try to find one subject that could turn into an internship, which I successfully did. Unfortuantely, due to some problems with HR which resulted in a very late posting of the offer, we haven't been able to find anyone for the internship.
Some time has passed since then and the annual salary negotiation left me quite unhappy, which my manager is well aware of. He said that he will do everything he can to fix this next year, but considering the explanation I've got this year concerning my raise, I have some hope about this, but not that much. So I'm actually having a look at other positions, without considering me actively looking. He's not aware of that, as things may get better next year and I don't want to appear as threatening him with a potential resignation.
Problem is that in the past few days, he has been actively pushing me to take an intern on another subject (perfectly related to my area, spontaneous application) for around 6 months which is for me a period of time during which I may hand him over my resignation, leaving the intern with no tutor, which is something I wouldn't like to do to anybody. How to handle this the most professionally way ?
Edit : Thanks to the good answers. I think I'll take this opportunity as this is something I already wanted to do before this spontaneous application. I'll let my manager handle the consequences of my resignation if the situation arises, it's his job after all.