Affection can be shown in a myriad of ways, and not cross people's sexual boundaries. I think as long as everyone is open and honest with themselves and each other, then things can work out. My wife and I are lesbians. We have an unfortunate habit of falling for straight girls. A lot of these straight girls are still in our life, because they are wonderful people and we enjoy their company. We love them and they love us. Some of them we kiss on the lips ( a family kiss, we call it), while other prefer that not happen. Some cuddle with us and even sleep in bed with us, others prefer their own sleeping quarters.
I don't know that it makes things "easier" to be bisexual. There are a lot of straight girls that make out or even have sex with other girls, for a myriad of reasons that have nothing to do with being bi or lesbian.
I think as long as you're secure in yourself, you can be in whatever kind of relationship with whomever you want. Some friends of ours include a woman with her two husbands. The husbands have been intimate once or twice, but don't identify as gay. Mostly they are 'brothers', and they take pleasure in both caring for their mutual wife.