I think "in out in out" is all wrong. Just push it in and then keep it there. What's with all this "in out" nonsense.
In my experience it doesnt necessarily break a relationship but can depend on the sexual desires of the woman you are involved with especially if they are more voracious than passive. I have a very tiny penis and if the woman in question was used to much better endowments even if other sex play was good they tended to at least wish I had more to give in the size department. In general however I think the size doesnt matter holds true especially if the non sexual part of the relationship is strong. I dont think most women are 'size queens' and even if they have a preference they dont think of themselves that way and are not necessarily exclusive. I have definitely known some that were not exactly enticed by the knowledge that I have a very tiny cock but those that got to know me otherwise were (at least initially ) not completely put off by my underendowment - surprised yes, disappointed? probably a little but automatically dismissive rarely.