Complex sentence: Impressed, Stacey begins a new friendship with Mike by apologizing for their prior run in but explains that he was protecting his sister, and, seeing how much Mike likes her, gives him advice on how to win her heart.
Split into simpler sentences: Impressed, Stacey begins a new friendship with Mike by apologizing for their prior run-in. However, he explains that he was protecting his sister, and, seeing how much Mike likes her, gives him advice on how to win her heart.