Having a larger than normal erection due to the fact you would like to start a family and have a life with your partner. This is often because you are head over heels in love with the person and see beauty in everything they do.
Six months into knowing Yuki, Alexander is more in love than he ever was. When she walked in the room he began Pitching A Family Tent, knowing that they weren't about to just have sex; they have sex with their future in mind.