Jealousy on my part or inappropriate behavior on theirs?

I have a friend who is the mom of my toddler's friend. She is not married and is separated from her daughter's dad, but is dating. We occasionally have playdates together. Whenever we get-together, if my husband is around, she only chats with my husband, mostly about plants, which my husband loves to give advice on. But I am often left wondering, does she have any interest in me or does she come over just to hang out with my husband? To make matters worse, firstly my friend is very pretty, and secondly, my husband seems to pay a lot of attention to her, and seems to really enjoy all her gardening questions. When we are all together, I often attend to the kids' needs, and they carry on an adult conversation as if the kids and I weren't even in the background! I am not a jealous or possessive kind of woman, but it does bother me to feel left out from these conversations, especially when I am left to wonder not only if my husband is attracted to my beautiful friend (who almost always wears revealing clothes when she visits even when the weather is cold) but also if my friend feels flattered by all the attention she receives from my husband. Especially because she hasn't settled down with a guy, I feel that perhaps she has a need to feel like she is desirable, but if she seeks that affirmation from my husband, it is not fair to me. Now, I have refered to her as my friend, but we are not really close. We only get together so the children can play together - they have known each other since they were born. For that reason, I always agree to meet with her when she suggests it. I always tell myself to rise above these emotions I get after most playdates when I am left feeling like this, and when I talk to my husband, he tells me I am overreacting over nothing. And he blames me for even inviting her over, if that's how I feel about her. However, I feel that it should not be my fault to agree to these playdates. It is my husband who should act sensitively and not pay so much attention to another woman in my presence, and especially since she is so pretty. I don't share his pion for gardening, but am I wrong to feel hurt by these events? Is not agreeing to have her over really the only solution to this?