Am I being petty and pregnant or should i really be upset?


So my partner has 4 children by another woman in which I have been in their lives since their oldest was born she's now 12(him and I grew up together I've known him since I was 4). We have been living together for 8 years now( I have yet to see or hear about a ring) and we are expecting our 2nd child together this year. So down to the nitty gritty.... On Thursdays he goes to play basketball with his friends, I don't mind at all because everybody needs to get out and do something with themselves. So I randomly do phine checks in my 10 year old phone just to monitor what she does, thus particular time I went into her ooVoo app to see what her and her little friends talk about. Once I opened the app I immediately seen messages to and from boys about dating and phone calls that were being held at 1,2, &3 in the am. After reading thru the messages i noticed it wasn't my daughter's account it was his daughters. So I showed him the messages and phone calls (now just to clear this up before asked, I pay our families cell phone bill). The next day I came home from work and I asked if he had spoken to her mother in regards to the situation he said yes but gave very vague details( which didn't bother me because he doesn't have a good memory). So about three days later, a Thursday, his basketball day, I get off of work and he picks me up from the train. The first thing he said when he got in the car was "You know I'm going to to play bball tonight", I'm like "okay, I'm cool with that." so he leaves home around 6:15pm. And doesn't make it back until 10pm. While he was gone I called him to ask if he would bring me some ice cream home because I was craving it lol but during our convo I heard children in the back ground and him raising the car window( his phone was attached to the Bluetooth in the car). So when he got home I asked out of curiosity, "did you really go to bball practice?" He's like "yeah, why you asked that?" So I explain why I had doubts. Due to me having complications I missed work for four days and went to the ER so those four days I would hint around how I just felt like he didn't go. At one point he got so upset and said " You don't like when I question you or accuse you of something you didn't do so why would you do it to me?" He was right so I didn't speak of it anymore. We go to pick up his children last Saturday and he calls their mom to let her know we are pulling up (just to remind you, she was on speaker because his phone is attached to the cars Bluetooth). She calls back to remind him something about the kids and then asks him "Are you alone?" He says "No", she then goes "ughhhhh okay bye". So now I'm like wtf? Why does it matter if you were alone or not? In his defense he says " maybe she was going to come out and talk about the kids", my response "What is it about the kids she had to say to you that I can't hear? I take care of these four children just as well as you two do!" (just to remind you, I DONT HAVE A RING). I dropped the convo because the kids were getting in the car. So the next day which was Sunday I get ready to go to Walgreen's to pick up my prescription, I asked his daughter of she wanted to tag along , of course she did. So we are driving to Walgreen's having the convo about her phone activities and I was letting her know I'm turning her phone line off until I can trust her( if her parents get her a phone that's on them but I'm not spending money on a 12 year old to have convos all times of the night). She then says "I knew I was in trouble when both of my parents were at school to pick me up". I respond asking "When was this?" "Last Thursday" she says back. Then she spills everything without me asking. Shes said, I made it back from my field trip around 7 pm and they were both there to talk to me. They dropped me off at home I went in the house and they were outside for a while. I then changed the subject for one she is a child and I wouldn't put her in an awkward position nor question a child about grown people's business, and second because I was getting pissed!!! I get home and asked him why did he lie to me and he says "I didn't, I went to basketball and then over there afterwards". Basically I'm upset because not only did he lie (several times in my opinion because I kept hinting around it) but he had his kids mother in my car driving her to and from where they were going. This is a person who has never invited me to a birthday party she's thrown for the kids(I've had her at my house for one of the kids bday and for Christmas so she could she her children, I'm not a petty person when it comes to children I try to do whats best for them), nor has she been cordial with me. So why would it be okay for her to be in my car especially without my knowledge? I'm just so pissed at him I'm about ready to leave and say eff trying to build with someone.

Now just to set the record straight I don't mind them getting together to talk to their child, I feel it should be done more often. My issues is I wasn't informed so I feel as though they were trying to do something else behind my back.