Boyfriend, and daughter

Lately my almost 4 year told is all about my boyfriend. He's been in her life for a little over a year now, and she talks about him all the time. She will she misses him, and I love you to him. We picked her up from school one day and she ran passed me, and give him a big hug. If he calls me she will talk want to talk him. She will tell me to call him... Is it okay that I let them have a close relationship? Her father is hardly around. He hasn't seen her once this year, and maybe twice later year. The only other two males in her life is my own father, and they are very close, and her uncle(she sees him about once a month)